This Non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2003-095481 filed in JAPAN on Mar. 31, 2003, the entire contents of which are hereby incorporated by reference.
The present invention relates to a pneumatic tire, more particularly to a bead structure capable of improving steering stability and ride comfort.
In general, a vehicle wheel rim on which a pneumatic tire is mounted has a counter which is specified according to the tire size and use, by a standardization organization or association in each country or region such as JATMA (Japan and Asia), T&RA (North America), ETRTO (Europe) and STRO (Scandinavia). In case of a passenger car tire for example, as well known in the art, its approved or recommended rim has a bead seat tapered at a small angle and a flange whose radially outer portion is curved axially outwards. Therefore, a pneumatic tire is conventionally designed such that the bead profile fits to such rim contour as shown in FIG. 8. To be concrete, the axially outer side face Sw is formed by a vertical portion 51 and a curved portion S2. The vertical portion S1 is parallel with the tire equatorial plane so as to fit the vertical lower portion of the rim flange Rf. Because the radius of curvature of the curved portion of the rim flanges Rf is about 10 mm (7.5 to 12 mm in JATMA) in case of passenger car tires, the radius of curvature of the curved portion S2 is set to be almost same but slightly larger than that of the rim flange consciously for example set in a range of about 10 to 20 mm so as to accommodate to variation of the flange curvature. Therefore, as shown in FIG. 8, a wedge shaped gap is formed between the curved portions of the bead and rim flange although no gap is formed between the vertical portions of the bead and rim flange.
On the other hand, in case of a very low aspect tire which is nowadays widely used in the high performance passenger cars, sports cars, etc., in order to improve steering stability, usually, the rigidity of the bead portion and lower sidewall portion is increased by increasing the volume of the bead apex rubber (b) and/or providing an additional cord reinforcing layer (c). As a result, because of the small sidewall portion, a portion which can function as a shock absorber is small, and deterioration of ride comfort is inevitable. Further, an increase in rubber volume and addition of cord layer are not always preferable from a point of view of heat buildup and rubber/cord separation.